1. Field
The described technology relates generally to a thin film transistor, a manufacturing method of the thin film transistor, and an organic light emitting diode (OLED) display including the same.
2. Description of the Related Art
Generally, a polysilicon layer can be applied to a high electric field mobility and high-speed operation circuit and can be configured of a CMOS circuit. As such, a polysilicon layer has been mainly used as a semiconductor layer for a thin film transistor. The thin film transistor using the polysilicon layer may mainly be used for an active device for an active matrix liquid crystal display (AMLCD) and a switching device and a driving device of an organic light emitting diode (OLED).
A solid phase crystallization method and an excimer laser crystallization method are used as a method of crystallizing amorphous silicon into polysilicon. Solid phase crystallization is a method in which the amorphous silicon layer is annealed at the temperature of about 700° C. or less, which is the deformation temperature of the glass that forms the substrate of a display element. The display element uses the thin film transistor for several hours to several tens of hours. The excimer laser crystallization is a method in which the silicon layer is locally heated and crystallized at the high temperature for a very short time by injecting the excimer laser to the silicon layer. However, the solid phase crystallization method has a problem of long process time and is performed at a high temperature for a long period of time so that a substrate may be deformed, and the excimer laser crystallization method has a problem of using an expensive laser device and protrusions are formed at a crystallized surface so that an interface characteristic between the semiconductor layer and the gate insulating layer is deteriorated. Thus, a method for crystallizing an amorphous silicon layer using a metal catalyst has been actively studied because the method is more advantageous in crystallization at a lower temperature within a short period of time to the solid phase crystallization method. The crystallization method using a metal catalyst includes a metal induced crystallization (MIC) method, a metal induced lateral crystallization (MILC) method, and a super grain crystallization (SGS) method.
However, in a semiconductor layer crystallized using a metal catalyst, the catalyst remains in a channel area so that a leakage current may be increased. Thus, an additional gettering metal layer is formed on the semiconductor layer to prevent the leakage current, and a gettering process is performed to remove the metal catalyst in the semiconductor layer by moving the metal catalyst to the gettering metal layer through a getting heat treatment.
The additional process for removing the gettering metal layer increases manufacturing costs complicates the manufacturing process, thereby causing a process failure.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.